The present invention relates to a photothermographic material. In particular, the present invention relates to a photothermographic material for scanners, image setters and so forth, which is particularly suitable for photographic art. More precisely, the present invention relates to a method for producing a photothermographic material that shows low temperature and humidity dependency during development for character line width (practice sensitivity).
There are known many photosensitive materials having a photosensitive layer on a support, with which image formation is attained by imagewise light exposure. Those materials include those utilizing a technique of forming images by heat treatment as systems that can contribute to the environmental protection and simplify image-forming means.
In recent years, reduction of amount of waste processing solutions is strongly desired in the field of photographic art from the standpoints of environmental protection and space savings. Therefore, development of techniques relating to photothermographic materials for photographic art is required, which materials enable efficient exposure by a laser scanner or laser image setter and formation of clear black images having high resolution and sharpness. Such photothermographic materials can provide users with simpler and non-polluting heat development processing systems that eliminate the use of solution-type processing chemicals.
Methods for forming images by heat development are described in, for example, U.S. Pat. Nos. 3,152,904 and 3,457,075 and D. Klosterboer, xe2x80x9cThermally Processed Silver Systemsxe2x80x9d, Imaging Processes and Materials, Neblette, 8th ed., compiled by J. Sturge, V. Walworth and A. Shepp, Chapter 9, p.279, (1989). Such photothermographic materials comprise a reducible non-photosensitive silver source (e.g., silver salt of an organic acid), a photocatalyst (e.g., silver halide) in a catalytically active amount and a reducing agent for silver, which are usually dispersed in an organic binder matrix. While the photosensitive materials are stable at an ordinary temperature, when they are heated to a high temperature (e.g., 80xc2x0 C. or higher) after light exposure, silver is produced through an oxidation-reduction reaction between the reducible silver source (which functions as an oxidizing agent) and the reducing agent. The oxidation-reduction reaction is accelerated by catalytic action of a latent image generated upon exposure. The silver produced from the reaction of the reducible silver salt in the exposed areas shows black color and provides contrast with respect to the non-exposed areas, and thus images are formed.
European Patent Publication (hereinafter referred to as EP-A) 762,196, Japanese Patent Laid-open Publication (Kokai, hereinafter referred to as JP-A) 9-90550 and so forth disclose that high-contrast photographic property can be obtained by incorporating Group VII or VIII metal ions or metal complex ions into photosensitive silver halide grains for use in photothermographic materials, or incorporating a hydrazine derivative into the photosensitive materials.
For use of photographic art films in the fields of newspaper printing, commercial printing and so forth, there have generally been desired systems that can provide stable images at any time. However, photothermographic materials showing such high-contrast photographic property as mentioned above, which is required for photographic art films, suffer from a problem that they show higher temperature and humidity dependency of character line width (practice sensitivity) during development compared with conventional films to be treated with chemicals.
Therefore, it has been desired to provide a photothermographic material that shows low temperature and humidity dependency of character line width during development and thus is suitable for use in photographic art.
Therefore, an object to be achieved by the present invention is to provide a photothermographic material that shows low temperature and humidity dependency of character line width (practice sensitivity), in particular, as a photothermographic material for photographic art, more specifically, a photothermographic material for scanners, image setters and so forth.
The inventors of the present invention assiduously studied in order to achieve the aforementioned object. As a result, they found that an excellent photothermographic material that provides the desired effects could be obtained by using a compound represented by the formula (1) and a nucleating agent represented (by the formula (A), (B) or (C), and thus accomplished the present invention.
That is, the present invention provides a photothermographic material having an image-forming layer that contains a non-photosensitive silver salt of an organic acid, a photosensitive silver halide, a nucleating agent and a binder on at least one side of a support, wherein the material contains a compound represented by the formula (1) and the nucleating agent consists of at least one kind of compound represented by the following formula (A), (B) or (C): 
In the formula (1), P represents an oxygen atom, a sulfur atom or NH, Q represents an oxygen atom or a sulfur atom, Y represents OH, OM (M represents a counter ion) or NH2, L represents a divalent bridging group, and Z represents an alkyl group, an aryl group or a heterocyclic group. 
In the formula (A) or (B), Z1 and Z2 each represent a nonmetallic atomic group that can form a 5- to 7-membered ring structure including Z1 or Z2, Y1 and Y2 each represent xe2x80x94C(xe2x95x90O)xe2x80x94 group or xe2x80x94SO2xe2x80x94 group, and X1 and X2 each represent hydroxy group or a salt thereof, an alkoxy group, an aryloxy group, a heterocyclyloxy group, mercapto group or a salt thereof, an alkylthio group, an arylthio group, a heterocyclylthio group, an amino group, an alkylamino group, an arylamino group, a heterocyclylamino group, an acylamino group, a sulfonamido group or a heterocyclic group. Y3 represents a hydrogen atom or a substituent. In the formula (C), Z3 represents an alkyl group which may have one or more substituents, an aryl group which may have one or more substituents or a heterocyclic group group which may have one or more substituents, W represents an aryl group which may have one or more substituents or an alkyl group substituted with an electron-withdrawing group, and M represents a counter cation.
The compound represented by the formula (1) may be added to the image-forming layer or a non-photosensitive layer on the same side of the support as having the image-forming layer. The photothermographic material of the present invention preferably has a film surface pH of 6.0 or less on the side of the support having the image-forming layer.
According to the present invention, there can be obtained photographic performance suitable for photographic art applications including smaller temperature and humidity dependency of character line width during development. Further, it enables coating with an aqueous system, which is advantageous in view of environmental protection and cost.